9,027 research outputs found
Tracing the Evolution of Physics on the Backbone of Citation Networks
Many innovations are inspired by past ideas in a non-trivial way. Tracing
these origins and identifying scientific branches is crucial for research
inspirations. In this paper, we use citation relations to identify the
descendant chart, i.e. the family tree of research papers. Unlike other
spanning trees which focus on cost or distance minimization, we make use of the
nature of citations and identify the most important parent for each
publication, leading to a tree-like backbone of the citation network. Measures
are introduced to validate the backbone as the descendant chart. We show that
citation backbones can well characterize the hierarchical and fractal structure
of scientific development, and lead to accurate classification of fields and
sub-fields.Comment: 6 pages, 5 figure
Coarsening Dynamics of a One-Dimensional Driven Cahn-Hilliard System
We study the one-dimensional Cahn-Hilliard equation with an additional
driving term representing, say, the effect of gravity. We find that the driving
field has an asymmetric effect on the solution for a single stationary
domain wall (or `kink'), the direction of the field determining whether the
analytic solutions found by Leung [J.Stat.Phys.{\bf 61}, 345 (1990)] are
unique. The dynamics of a kink-antikink pair (`bubble') is then studied. The
behaviour of a bubble is dependent on the relative sizes of a characteristic
length scale , where is the driving field, and the separation, ,
of the interfaces. For the velocities of the interfaces are
negligible, while in the opposite limit a travelling-wave solution is found
with a velocity . For this latter case () a set of
reduced equations, describing the evolution of the domain lengths, is obtained
for a system with a large number of interfaces, and implies a characteristic
length scale growing as . Numerical results for the domain-size
distribution and structure factor confirm this behavior, and show that the
system exhibits dynamical scaling from very early times.Comment: 20 pages, revtex, 10 figures, submitted to Phys. Rev.
Cosmic Microwave Background constraints of decaying dark matter particle properties
If a component of cosmological dark matter is made up of massive particles -
such as sterile neutrinos - that decay with cosmological lifetime to emit
photons, the reionization history of the universe would be affected, and cosmic
microwave background anisotropies can be used to constrain such a decaying
particle model of dark matter. The optical depth depends rather sensitively on
the decaying dark matter particle mass m_{dm}, lifetime tau_{dm}, and the mass
fraction of cold dark matter f that they account for in this model. Assuming
that there are no other sources of reionization and using the WMAP 7-year data,
we find that 250 eV < m_{dm} < 1 MeV, whereas 2.23*10^3 yr < tau_{dm} <
1.23*10^18 yr. The best fit values for m_{dm} and tau_{dm}/f are 17.3 keV and
2.03*10^16 yr respectively.Comment: 17 pages, 3 figure
Dynamics of Ordering of Heisenberg Spins with Torque --- Nonconserved Case. I
We study the dynamics of ordering of a nonconserved Heisenberg magnet. The
dynamics consists of two parts --- an irreversible dissipation into a heat bath
and a reversible precession induced by a torque due to the local molecular
field. For quenches to zero temperature, we provide convincing arguments, both
numerically (Langevin simulation) and analytically (approximate closure scheme
due to Mazenko), that the torque is irrelevant at late times. We subject the
Mazenko closure scheme to systematic numerical tests. Such an analysis, carried
out for the first time on a vector order parameter, shows that the closure
scheme performs respectably well. For quenches to , we show, to , that the torque is irrelevant at the Wilson-Fisher fixed
point.Comment: 13 pages, REVTEX, and 19 .eps figures, compressed, Submitted to Phys.
Rev.
Lamellae Stability in Confined Systems with Gravity
The microphase separation of a diblock copolymer melt confined by hard walls
and in the presence of a gravitational field is simulated by means of a cell
dynamical system model. It is found that the presence of hard walls normal to
the gravitational field are key ingredients to the formation of well ordered
lamellae in BCP melts. To this effect the currents in the directions normal and
parallel to the field are calculated along the interface of a lamellar domain,
showing that the formation of lamellae parallel to the hard boundaries and
normal to the field correspond to the stable configuration. Also, it is found
thet the field increases the interface width.Comment: 4 pages, 2 figures, submitted to Physical Review
Optimal Location of Sources in Transportation Networks
We consider the problem of optimizing the locations of source nodes in
transportation networks. A reduction of the fraction of surplus nodes induces a
glassy transition. In contrast to most constraint satisfaction problems
involving discrete variables, our problem involves continuous variables which
lead to cavity fields in the form of functions. The one-step replica symmetry
breaking (1RSB) solution involves solving a stable distribution of functionals,
which is in general infeasible. In this paper, we obtain small closed sets of
functional cavity fields and demonstrate how functional recursions are
converted to simple recursions of probabilities, which make the 1RSB solution
feasible. The physical results in the replica symmetric (RS) and the 1RSB
frameworks are thus derived and the stability of the RS and 1RSB solutions are
examined.Comment: 38 pages, 18 figure
The reinforcing influence of recommendations on global diversification
Recommender systems are promising ways to filter the overabundant information
in modern society. Their algorithms help individuals to explore decent items,
but it is unclear how they allocate popularity among items. In this paper, we
simulate successive recommendations and measure their influence on the
dispersion of item popularity by Gini coefficient. Our result indicates that
local diffusion and collaborative filtering reinforce the popularity of hot
items, widening the popularity dispersion. On the other hand, the heat
conduction algorithm increases the popularity of the niche items and generates
smaller dispersion of item popularity. Simulations are compared to mean-field
predictions. Our results suggest that recommender systems have reinforcing
influence on global diversification.Comment: 6 pages, 6 figure
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